1. Field of the Invention
The present invention relates to a transmission control method for a continuously variable transmission. More particularly, the present invention relates to a transmission control method for a continuously variable transmission for enhancing the response of the transmission attendant on a driver's accelerating/decelerating operation.
2. Description of Background Art
As a continuously variable transmission for use in a vehicle such as a motorcycle, a hydraulic type continuously variable transmission has been known. See, for example Japanese Patent Publication No. Hei 08-006797; Japanese Patent Laid-open No. 2006-200727 or Japanese Patent Laid-open No. 2007-016967.
The hydraulic type continuously variable transmission basically uses the control of a target engine speed in which transmission gear ratio is changed according to the difference between an actual engine speed (rpm) and the target engine speed. More specifically, when the actual engine speed is lower than the target engine speed, the transmission gear ratio is lowered so as to raise the actual engine speed. When the actual engine speed is higher than the target engine speed, on the other hand, the transmission gear ratio is raised so as to lower the actual engine speed.
In the target engine speed control as above-mentioned, the transmission gear ratio is changed at the time when a difference is generated between the actual engine speed and the target engine speed. Therefore, a time lag may possibly be generated between a change in the position (angle) of a throttle valve varied according to the driver's accelerating/decelerating operation and a change in engine speed. More specifically, on one hand, the position of the throttle valve is usually changed directly according to an operational amount of a throttle grip or an accelerator pedal. As above-mentioned, in the target engine speed control, on the other hand, the actual engine speed is varied by changing the transmission gear ratio while checking the difference being generated between the actual engine speed and the target engine speed, so that the change in the engine speed is delayed behind the change in the position of the throttle valve.
Such a phenomenon is not limited to hydraulic type continuously variable transmissions but is similarly generated also in other continuously variable transmissions such as frictional type continuously variable transmissions (belt-type continuously variable transmission, toroidal continuously variable transmission, etc.) and electric power type continuously variable transmissions.